Hydraulic motor actuated marine propeller pitch control



March 9, 1954 J, Q ALMEN 2,671,518

HYDRAULIC MOTOR AC'I'UATED MARINE PROPELLER FITCH CONTROL Filed March 28, 1950 3 Sheets-Sheet l Simentor (5i/7 @MyW/7 Gttornegs HYDRAULIC MOTOR ACTUATED MARINE PROPELLER PITCH CONTROL 5 Sheets-Sheet 2 J. O. ALMEN .NlTU u r. w. C l m a m N H// uw 3@ a n w/ 3 ,.n J M u 1/ I '[III 1|. III lllllllldlnl, QN MTL @N .mm B N\\ N N .R \.\m\\\\ Y I. `.\\WM\= u. m su w Cw N RRQ@ R l s* lvm March 9, 1954 Filed March 28, 1950 March 9, 1954 J, o, ALMEN 2,671,518

HYDRAULIC MOTOR ACTUATED MARINE PROPELLER FITCH CONTROL Patented Mar. 9, 1954 HYDRAULIC MOTOR ACTUATED MARINE YPROPELLER PITCH CONTROL `lohn .0. Almen, Royal 0ak, Mich., assigner to General Motors Corporation, Detroit, Mich., a

corporation of Delaware .implication March 28, 1950, Serial No. 152,379

1I) Claims. l

This invention relates toY marine propeller drive mechanisms and more particularly to a fluid pressure actuator means for changing propeller blade pitch.

Anobject of thisinvention is to provide a propeller blade pitch controlmechanism normally operable through fluid pressure actuation ncor porating means whereby the propeller pitch may be set manually in the event of fluid pressure failure.

Another object of thisinvention is to provide a reduction drive and power delivery system in which means are provided for changing propeller pitch with simple, direct axial motion and incorporating a neat compact compartmenting of the units which provide these advantageous .features for superior accessibility as well as for lubrication.

A further object of thisinvention is to provide a novel follow-up arrangement of pitch control mechanism involving fluid pressure valving and piston actuation which avoids creepvand affords positive stationing of the control elements while giving rapid response when rapid shift is desired.

Still another object of this invention is to provide a balanced pressure condition for the fluid pressure servo system used to actuate and to hold propeller pitch change which avoids the need `for constant force and stresses to be dealt with Vby the servo means.

An additional object of this invention is to s provide in a servo mechanism of the class described, a piston having an annular inlet passage positioned intermediate spaced annular rbosses in which the bosses are longitudinally so spaced as to meter inlet pressure utilized to cause movement of the piston in such a manner as to prevent pounding and shock as the piston approaches either extremity of its permissible length of travel.

These and other objects and advantages of this invention will bel apparent from thevfollowing description and claims taken in conjunction with the following drawings in which:

Figure l is a side elevation of theinvention as installed in a ship, with the propeller hub sectioned to show details of `thepitch shifting mechanism.

Figure 2 is a vertical elevation of the pitch shift and actuator mechanism of Figure l in whiehthe servo mechanism is taken substantially along the line 2-2 of Figure 5.

Figure 3 is a vertical cross section taken generaliy along the line ii-B of Figure 2 `including a section of the ball joint between the lever and the valve.

Figure 4 isapartlsection takenat .Ll-4 of Figure 2.

(Cl. YZO-160.37)

Figure 5 is a crosssectiontakenat 5-l5 oiFigure 2.

kFigure 6 is a partial .transverse sectional View of the servo pump device taken at 6-6 of Figure'l.

Referring to Figure 1, `there is shown altransmission housing IDU, cover plate IUI, servo control housing Ill2, stub-shaft housing ID3, vcontrol handle 59, propeller or load-shaft I I, propeller hub i2, propeller blade |05, rudder control'housing IM, rudder IM and servocylinder L08. Propeller shaft II is splined to propeller hub I2 at iii@ so that the hub rotates in a single direction along with propeller shaft'I I. Positionedwithin hollow load shaft I I is blade shifter rod I3, which, as explained hereafter in further detaiLispo'sitioned to move longitudinally with respect "to shaft l I to cause changes inpitch'of the Vpropeller blades. A rack I4 on one end of shift rod t3 and positioned within propeller hub I2, cooperates with teeth (not shown) on the propeller blade stub shaft IIIB to vary the pitchof theblade. While only a single blade is shoWn,-it'will'readily be understood that two or moreiblades Would vbe used to make upthe propeller. The rackand its relation to the propeller'stub shaft/per se is fully disclosed and described inthe-patent `to Edward V. Rippingille 2,374,833 issuedlMay 4l, 1945,and does not constitute a part ofthis invention. The transmission, servo control and 'stubfsha'fthousings and cover plate I0! Aare bolted together -as shown to provide easyassembling and servicing of thedevice.

Referring to Figure 2, there is shown apower shaft I adapted to-be connected to an engine shaft (not shown) 'having aflixed thereto an external gear 2, the sleeve 2a of which fis supported in bearing 3 held in ange luna of casing Hill. Gear 2 meshes with an internal gear 4 xedron one end of an intermediate stub drive shaftf, which drive shaft is supported in abeari-ng't held .by flange mia of casing I G2. Shafts I and' are therefore disposed parallel to Aeach votherbutfare offset so that the center lines of the'shaftsare nonconcentric. Body l, held in bearing t Vof housing H62 is splined to drivefshaft Suso 'as to rotate with the shaftA and is bolted to clamp member le which in turn, drives hollowlpropeller. shaft Ii fixed to propeller hub I 2 of Figure .1. -Gears '2 and 4 are lubricated through a passage 'Ill drilled in stub shaft 5 inside of bearing-'16.

Blade shifter rod I3 is slidably*supportediinside hollow load shaft II for axial movement andi-extends to the left through clamp member 1|.01and terminates in a ilanged member I5. Member V.I5 is connected by threek rods vI6 (see Figurei) -to'a collar Il slidably positioned'uponshaft. Thus,

3 any reciprocating movement that may be applied to collar I1 is transmitted to shift rod I3 through rods I 6 and flange member I5.

As will be understood further, shifting of collar II by the blade pitch control means reciprocates rack I4 on the end of shift rod I3 to change and to hold the pitch of the propeller blades for all conditions of operation, including no-drive, forward, and reverse drive of the vessel.

A seal I8 is fitted between housing web |021) of casing |02 and splined body 'I to prevent leakage of bilge water into bearing 8 and the interior of the housing.

It is important to note a unique feature of this mechanism, namely, the arrangement of collar I1, rods I6, flange member I5, and sea1 I8 with respect to bearing 8. By this arrangement, the means by which the pitch shift means is actuated, including rack I4, operates inside of or through the bearing 8. Thus, a compact, durable, strong, and yet relatively light mechanism is provided which may be quickly and easily assembled or disassembled in the event that servicing is required.

A shift collar I9, fitted into the annular U- shaped groove of collar is actuated to impart axial motion to collar I'I, rods I6 fixed in collar I1, member I5, and shift rod I3.

As shown particularly in Figure 3, an actuator lever 2| is provided for imparting motion to shift collar I9. A cross shaft 20 pivotally mounted in housing |02 is attached to actuator lever 2| and provides a pivotal support for forked extensions 2| a drilled out to receive studs |9a provided on shift collar I9.

Since the forces necessary to adjust the propeller pitch are greater than can conveniently be overcome by direct manual effort a hydraulic servo unit is utilized. The servo unit includes a piston 23 sliding in cylinder 24 of housing |08. A hollow piston rod 22 extends through a bushing 24a into the interior of housing |02 and is pivotally connected to actuator 2| by means of studs 25. As will be understood, fluid pressure applied to move piston 23 in cylinder 24, to station the piston at various selected positions in the cylinder, wil1 cause collars I9 and I'I and, through the mechanism described, rod I3 and rack I4 to assume and hold different pitch for the drive of the propeller.

Hollow piston rod 22 encloses a valve mechanism 30 slidably positioned therein for compelling the piston under inuence of directed fluid pressure to occupy positions in which the pressure on both sides of piston 23 is equalized. For this operation, piston 23 is provided with an annular space 26 connected by a suitable port B8 with a cylinder feed pressure port 27 which, in turn, is connected to a source of fluid pressure as may be supplied by a pump further described in connection with Figure 6. Armular space 26 communicates with a passage 28 drilled through the head of piston 23. A port 29 in the side wall of hollow piston rod 22 opens into the port 3| of valve member 30, to admit uid pressure from passage 28 to the right hand side of piston 23 when valve 30 is moved to the left. As shown in Figures 2 and 5, a pair of discharge passages 33 and 35 are drilled in piston 23 to permit fluid pressure from the left side of the piston to escape. When the valve 30 is moved to the left to admit fluid pressure to the right hand side of piston 23, port 32 of the valve body registers with passage 35 of Figure 5 to admit discharge fluid into the interior of the hollow portion of valve 30. The discharge fluid thereupon passes through port 36 to hollow bore 36a, and hence past the radially spaced bosses 31 to the interior of housing |02.

For movement of piston 23 to the right, valve 30 is moved to the right, thereby connecting passage 28 to the left hand side of piston 23 through port 38 in the side wall of piston rod 22 and valve port 39. Fluid pressure from the right hand side of piston 23 is permitted to escape through drilled passages 40 and 40a (see Figure 5) drilled in piston 23. Port 4| in valve 30 is positioned to register with port 4|a in the piston valve Whenever ports 28 and 39 are in communication, thereby permitting discharge pressure from the right hand side of cylinder 23 to pass to the interior of the valve, through port 36, chamber 36a to the housing |02. The pump 60 of Figure 6 drains from casing |00 as a sump. Oil in the bottom of housing |02 is permitted to pass to housing |00 through passage |04 in the flange I02a.

It will be understood that when valve 30 is moved to lead the porting of rod 22, as described, piston 23 will continue to travel (to the left or right as the case may be) until the valve 30 blocks olf pressure in passage 28, at which time the piston comes to rest in a given position such that the pump pressure is sealed off and the piston-to-valve relationship is stabilized at a new position. The outlet ports from either side of piston 23 are blocked off at the same time the passage 29 is out off from either of the inlet ports 3| or 39 so as to trap fluid pressure both to the right and to the left of piston 23 to maintain the piston in its desired position in cylinder 24. Since the fluid pressure acting on opposite faces of the piston is the same, the piston is simply xed at its desired location Without being subject to unbalanced fluid pressure forces as it maintains the propeller blades at any predetermined pitch.

It is important to note the relationship of the spaced annular bosses 66 and 6`| and the length of annular passage to port 68. As will be apparent in Figure 2, piston 23 is capable of traveling from one end of cylinder 24 to the other. It is highly desirable that any sharp or hard impact of piston and either end of cylinder 24 be avoided. Bosses 66 and 61 and the length of annular passage 26 are so arranged that one of the bosses (depending upon the direction of travel of the piston) will partially cut off port 68 to meter inlet pressure fed to passage 26 as the piston approaches an end of cylinder 24. Thus, in the position shown, boss 65 partially cuts off inlet port 68 as the piston approaches the right hand end of the cylinder. The piston 23, therefore, will reduce its rate of travel as it approaches the end of the cylinder even though valve 30 may be positioned to admit inlet pressure to the left hand side of piston 23. In this manner, pounding and sharp impact of the piston on either end of the cylinder is avoided. It will further be understood that at no time do either of the annular bosses 66 or 6l completely block off port B3, and that the bosses merely act to meter the inlet pressure to provide for reduced rate of travel of the piston as it approaches either end of c' linder 24.

The leftward end of valve 30 terminates in a slot 42 and is located in fork 43 of lever 2| as best disclosed in Figure 3, to accommodate ball end 44 of lever 45 freely pivoted on cross shaft 4.6 mounted in casing |02.

ly intoV thefcasing |011;V Aspiring t51.4is,.dispos.edl

intermediatelevers 45iand14l toprovide a lost motion'A connection, the, spring being. wound around shaft lwyvithl its endsdepending. down,-` Wardly to engageblaterally extendingtbossesjl and 540,011.A levers? 45 `and (41, respectively.,- This arrangement permits the. external `control, mech-y anismv to maintai-na lead over :the follower action of ,the pistonand rod system.` Since the spring, 5I -engagesboth ,levers,45, and 41 lever, 45Wil1; berotated about shaft 45 by the downwardlyI extending Lendsof` the. spring, whenever lever 5B; issmoved toa 4new p0sition.-

It is likewiseprovided that in thef case, ofl fluid pressure failure, a clamp bar 53, shownvin Figure 3,` may rbesclamped .on ,one end pf. crossv vshaftl-Z to manually rock lever 2i ,to changeE bladepitch. Figure -ashows the arrangement of the vvarious partsrat the left end of.` valve,30,.in more detail. As .,shown,`v rod- ,22 lcarries studs .25, pivotallyiconnecting therrod to, lever# I pWhilesvalve -is pinned bymeansof'pin 55 (see also FigurelZ) to. forkl43,

Figure 6 -shows a, pump Yassembly Sil, driven fromffgear SG-keyed-to shaft i. Smallgear'l keyed to. crossshaftimesheswith and is driven bygear `56; thereby/drivingshaft 58and primary gear 59 of the pump. Pump. idler gear El mounted on stub j-shaft 62 ,-and gear. 59create oil pressure-in output passage 63 which in turnis connected,by-,a.,pip e r(notfshown) to port l2l.in the top ofservo cylinder24 of Figure-2. The pump zdrawspil from casing IUE through suction pipe 64 anddelivers-.it to, passage 63 under pres- .novelbladepitchcontrol mechanism which is particularlyadapted to beactuated byffluidv pressure but `which may manually be actuated in `the event of fiuidpressure failure; Itis believed tto be particularly noveltoposition theactuating meansscfthat-,it is supportedbyandextends 1 throughla bearing asshown. Such an arrangement isgadvantageous in-thatv it is strong-,and compactandyetcan be.y quickly and-easily.` assembled `and disassembled :forf service or--inspection. The various ,housingsandthe-,functional f machinery venclosed therein may also loe-quickly assembled Aor disassembled asi desired; Themachinel is, therefore,l particularlydesignedtofacilitate-quickrand sim-ple,l repair in :that any single-defective unit i mayA` be quickly*` replacedf The piston 2,3 is maintained in any desired position in the :cylinder through :the action of equal `duid pressure forces, acting. on opposite, facesof the piston, theY arrangementforming ,a -fluid ,pressure trap such thatcreep isfavoided,assis` the needffor constantly `maintaining -,a.. given .pressure directly from the fluid ,pressure source when the, valving is positioned to maintain the piston in a given position. In addition, the bosses, at .eachendof the. annular. passage-in t the` .servo piston are so positioned withrespect to the,- uid pressure inlet port as, to, reduce. .the eective. areaoftheinlet port as, the piston approaches either end ofthe cylinder. nthis` manner. all knockingand tsimck which might otherwise accrue is prevented.

'Blades-rockab eff Whetiis i ,claimed iis;

1.: InY midfiv C .tml systemfoljmerne pmpulsion, avariablepitcnclianee propeller, mecha.- nism .adapted'towprovid 'forward Yand* reverse propulsion fromapowerplant'Constantly rotatnsin .one direction,` ,a housing,y laterally spaced bearings in` Said housina-a ,power Shaft; va prvp/eller:v shaft,l a ,bushing connecting, saidj power shaft to saidpropeller shaft,` said'bushingextending through on,eo fsaic in bearings vfor support upon saidfhousingL shift rods extending through saidgbushing and ,said bearing .for reciprocating motion ,with respect ,therete for adjustingpro-v pelll Piton. a, Ilongitudinally reciprocable lcollar carried. by saidupowersshaft;connected to saidshift .rds,means co nrlectirlgjsaidV shift `rods to said propellerppitchuchange mechanism, a uid pressure source a, fluid pressure responsive servo, across, shaft supported -uponsaid housing, an actuator 'lever Vrotatably:mountedjupon said cross shatloperatively connected to said vcollar for imparting longitudinal motion to said icollar, ymeans operably connectingsaid vactuator, lever vto said servo, a ,manua lly,operablepropeller pitch selector, lever, andpa manually operable self-lapping valve havingma ported valve bodyjconnected to said propeller,pitch `selector'lever for controliing the admissionV of iiuijdjpressure to said servo, said valve hai/"ing` ,ported 'portion thereof "connected 4to said actuator @lever effective to bloclg off'gsaid Vports` to, trappressure lfluidin 'said'servo to positively maintainl lthe propeller pitch setting selectedby said Apropeller Apitch selector lever.

2. 'In actuation andjcontrol systems for marine propellers, thecombinati'on of 'an Iengine shaft, an intermediate shaithahollow,propeller shaft,- ahub andw hdiligible, propeller blades socketedf in said hubmveans havingvaconnection through said hollow shaftwith said bladesfor-controllably rocking' the`4 sameeto different; forward Vand-'reverse ypitch positions, means couplingY said intermediate Shaftand said''propellershaft, aV source of, fluid pressure; Ia, 'uidr pressure responsive motor operably connected, Jto` saidY propeller pitch control means,k said motor comprising a piston slidableinapprted cylinderand having ya piston rod' connectedjto saidA propeller pitch control means a`b1ore in said piston rod, passagefformiltg,meansy in saidjpistonfor admitting fluidpressurejfrom 'saidjsoure-tc saidpiston rod, a ported Valve body slidably; movabley in said piston rod Vfor controlling Athe vadmission of` pressure uid fromV saidV bore. to said-Huid motor, manually operable controlijmeans` for moving said'valve pogjly` independently of Vsaid 4piston rodfsaid valve body4 being effective in`one position` thereof in saidv4 piston 'roddto block` off -said ports to trap fluidpressure atjiopposite sides V'of `saidhpisten to maintain the rpropeller 'pitch setting determined by` said ,manuallyf'operable means,

3,. In Centrols.:ferychengins theptch Ofmafine propeller blades; the; Combinaties 0fj a. marine pr0ee1-1e1` Cons Jvne.; Qf e hub equipped..4 with oforwardgandreverse-pitch positionsmandjaghollow propellerl shaft containing a member; connected tojrockhsaidblades through equalansle, asaulefof uidfpressllra fluid Servo actuator, means operative uponsaid member to shiftandjo hold; said*l blades in selectedpitch p ositinrls,1saidl uid; servo actuator means coinprisinaylinder, ariston., and La .ported piston rod ,operativen connected to Saidblade rocking member.. Contrlmeans forseiduid Servo actuatorfeiive .tovarygpsonellerpitch Saidiontrol means comprising -a 'portedva'lve body positioned within said piston rod and movable to selectively direct pressure fluid from said source to opposite sides of said piston, said piston rod being effective in one position thereof to block off said ports to trap fluid pressure at opposite sides of said piston, a manual control connected to said valve body for selectively positioning said valve body to actuate said servo, and manual means operable independently of said uid servo to shift said propeller rocking member when said uid servo actuation means is ineffective.

4. In a drive control system for marine propulsion, a propeller pitch change mechanism adapted to provide forward and reverse propulsion, a housing, a power shaft extending through said housing and terminating adjacent one end of said housing, a propeller drive shaft, means including a body member connecting said power shaft to said propeller drive shaft, a bearing in said housing, an extension on said body member positioned between said bearing and said power shaft for support upon said housing, a propeller pitch control shaft connected to said propeller pitch change mechanism, a rod member extending through body member and movable with respect thereto, detachable means connecting said rod member to said propeller pitch control shaft, a collar carried by said power shaft connected to said rod member, and hydraulically actuated lever mechanism connected to said collar for moving said rod member through said body member to vary the propeller pitch.

5. In a drive control system for marine propulsion, a propeller pitch change mechanism adapted to provide forward and reverse propulsion, a housing, an engine driven shaft extending through said housing and terminating adjacent one end of said housing, a power shaft extending through the opposite end of said housing, gears on said engine shaft and said power shaft for drivingly connecting said shafts to each other, said housing having a detachable portion whereby said engine shaft and the gear carried thereby may be removed as a unit from the remainder of said housing, a propeller drive shaft external of said housing, a bearing in said housing, detachable means including a body member connecting said power shaft to said propeller drive shaft, said body member having a portion extending between said bearing and said power shaft for support upon said housing, a propeller pitch control shaft connected to said propeller pitch change mechanism, a rod member extending through said bushing, de-

tachable means connecting said rod member to I said propeller pitch control shaft, a collar cai'- ried by said power shaft connected to said rod member, a source of incompressible iiuid pressure, a fluid pressure responsive servo member operatively connected to said collar, and a manually controlled self-lapping valve for controlling the admission of uid pressure to said servo to determine the propeller pitch.

6. In a control system for controlling the pitch of marine propeller blades, a propeller having a hub equipped with blades rockable to forward and reverse pitch positions, a propeller pitch control shaft, mechanism connecting said propeller pitch control shaft to said propeller blades to control propeller pitch, a pump for supplying incompressible fluid under pressure, a uid pressure responsive servo motor having a piston and a pair of control chambers adapted to receive iiuid under pressure, a piston rod carried by said piston, means including linkage connecting saidpiston rod to said propeller pitch control shaft, manually movable control valve body within said piston rod, ports in said valve body and piston rod for controlling the admission of iiuid pressure and exhaust of uid pressure from said chamber, said valve body being effective in one position thereof to position said ports to admit fluid pressure from said pump to one of said chambers and to simultaneously connect another of said chambers to exhaust, said valve being movable to a second position to position said ports to connect said one chamber to exhaust and to connect said other chamber to said pump, said piston rod being movable by said piston to block oi said ports to trap said incompressible fluid in both of said chambers to maintain the propeller pitch setting selected by said valve body.

7. In a drive control system for marine propulsion, a propeller pitch change mechanism adapted to provide forward and reverse propulsion from a power plant constantly rotating in one direction, a housing, a bearing in said housing, a propeller drive shaft external of said housing, a power shaft extending through said housing, means including a body member supporting said power shaft and connecting said power shaft to said propeller drive shaft, said body member having a portion thereof positioned between said bearing and said power shaft for support upon said housing, a shift rod extending through said body member for reciprocatory motion with respect thereto, means connecting said shift rod to said propeller pitch change mechanism, a source of incompressible uid pressure, a uid pressure responsive servo having a piston and a pair of control chambers associated with said piston, a longitudinally reciprocable collar carried by said power shaft and connected to said shift rod, a piston rod fixed to Vsaid piston, linkage mechanism connecting said collar to said piston rod for reciprocating said collar, a valve body carried by said piston rod, manually operable means for moving said valve body with respect to said piston rod, and ports in said piston rod and said valve body for controlling the admission of fluid pressure to and exhaust of fluid pressure from said chambers, said valve body being effective in one position to align said ports to admit uid pressure to one of said chambers and to connect the other of said chambers to exhaust, said valve being eifective in a second position to align said ports to connect said one chamber to exhaust and to admit fluid pressure to said other chamber, said valve body being eifective in a third position to position said ports to trap incompressible uid in both of said chambers and to block off both of said chambers from said uid pressure source.

8. In a drive control system for marine propulsion, a propeller pitch change mechanism adapted to provide forward and reverse propulsion from a power plant constantly rotating in one direction, a housing, a bearing in said housing, a propeller drive shaft external of said housing, a power shaft extending through said housing, means including a body member supporting said power shaft and connecting said power shaft to said propeller drive shaft, said body member having a portion thereof positioned between said bearing and said power shaft for support upon lsaid housing, a shift rod extending through said body member for reciprocatory motion with respect thereto, means connecting said shift rod to said propeller pitch change mechanism, a

source of incompressible fluid pressure, a fluid pressure responsive servo having a piston and a pair of control chambers associated with said piston, a longitudinally reciprocable collar carried by said power shaft and connected to said shift rod, a piston rod fixed to said piston, linkage mechanism connecting said collar to said piston rod for reciprocating said collar, a valve body carried by said piston rod, manually operable means for moving said valve body with respect to said piston rod, and ports in said piston rod and said valve body for controlling the admission of fluid pressure to and exhaust of fluid pressure from said chambers, said valve body being effective in one position to align said ports to admit fluid pressure to one of said chambers and to connect the other of said chambers to exhaust, said valve being effective in a second position to align said ports to connect said one chamber to exhaust and to admit fluid pressure to said other chamber, said piston rod being movable by said piston to position said ports to trap incompressible fluid in both of said chambers and to block off both of said chambers from said fluid pressure source.

9. In a drive control system for marine propulsion, a propeller pitch change mechanism adapted to provide forward and reverse propulsion from a power plant constantly rotating in one direction, a housing, a bearing in said housing, a propeller drive shaft external of said housing, a power shaft extending through said housing, means including a body member supporting said power shaft and connecting said power shaft to said propeller drive shaft, said body member having a portion thereof positioned between said bearing and said power shaft for support upon said housing, a shift rod extending through said body member for reciprocatory motion with respect thereto, means connecting said shift rod to said propeller pitch change mechanism, a source of incompressible fluid pressure, a fluid pressure responsive servo having a piston and a pair of control chambers associated with said piston, a longitudinally reciprocable collar carried by said power shaft and connected to said shift rod, a piston rod flxed to said piston, linkage mechanism connecting said collar to said piston rod for reciprocating said collar, a valve body carried by said piston rod, manually operable means for moving said valve body with respect to said piston rod, and ports in said piston rod and said valve body for controlling the admission of fluid pressure to and exhaust of iluid pressure from said chambers, said valve body being manually movable in one direction to align said ports to connect one of said chambers to said fluid pressure source and to connect the other of said chambers to exhaust, said valve body being manually movable in the opposite direction to align said ports to connect said one chamber to exhaust and to connect said other chamber to said fluid pressure source, said piston rod being movable in response to motion of said piston to block olf both of said chambers from said fluid pressure source and to position said ports to trap fluid pressure in both of said chambers.

10. In a drive control system for marine propulsion, a propeller pitch change mechanism adapted to provide forward and reverse propulsion from a power plant constantly rotating in one direction, a housing, a bearing in said housing, a power shaft, a propeller shaft, a bushing connecting said power shaft to said propeller shaft, said bushing extending through said bearing for support upon said housing, shift rods extending through said bushing for reciprocatory motion with respect thereto for adjusting propeller pitch, a longitudinally reciprocable collar carried by said power shaft connected to said shift rods, means connecting said shift rods to said propeller pitch change mechanism, a source of incompressible fluid pressure, a fluid pressure responsive servo having ya piston and a pair of control chambers associated with said piston, a cross shaft supported upon said housing, an actuator lever rotatably mounted upon said cross shaft operatively connected to said collar for imparting longitudinal motion to said collar, a hollow stem connecting said actuator lever to said piston, a manually operable propeller pitch selector lever, a valve body connected to said propeller pitch selector lever positioned within said hollow stem member, ports in said stem and said valve body for controlling the admission of fluid pressure to and exhaust of iluid pressure from said chambers, said stem being movable in response to movement of said piston to position said ports to trap fluid pressure in both of said chambers to positively maintain the propeller pitch setting selected by said valve body.

JOHN 0. ALMEN.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 571,745 Brinkmann Nov. 24, 1896 766,953 Krebs Aug. 9, 1904 1,365,347 Schneider Jan. 1l, 1921 1,475,869 Petrie Nov. 27, 1923 2,010,640 Michl Aug. 6, 1935 2,244,770 Englesson June 10, 1941 2,374,833 Rippingille May 1, 1945 2,480,521 Thompson Aug. 30, 1949 2,495,493 Herresho Jan. 24, 1950 

